Electronic circuits are, of course, extremely well-known. Typically, an electronic circuit is manufactured in a particular configuration and the subsequent operation of the circuit is determined by that configuration. Typically, no modification of that configuration (and in particular, no modification of individual components) is possible after manufacture. The resistance of resisted elements in such circuits is typically fixed during manufacture, and those resistance values are not modifiable later on.
A wide variety of data storage and retrieval systems are also known, using a wide variety of techniques for storing data on a variety of storage media. There is an on-going need with such systems to find ways in which data may be stored securely, i.e. in a manner such that it is not readily apparent that data has been stored, and furthermore what that data is.